The prior art, as evidenced by U.S. Pat. Nos. 3,652,639; 3,875,258; 3,950,317, and U.S. Pat. Nos. Re. 28,715; 29,014 and 33,291, teaches the preparation of graft polymer dispersions, which are useful in the preparation of polyurethanes by the polymerization of ethylenically unsaturated monomers in the presence of polyols. The above patents disclose various methods of preparing graft polymer dispersions. U.S. Pat. No. 3,931,092 teaches the preparation of polymeric solids by polymerizing in the presence of a free-radical initiator and an organic solvent. The solvent concentration employed is from about 1 part to 19 parts by weight per part of the hydroxy-terminated organic compound, which has a polymerizable carbon double bond. U.S. Pat. No. 3,953,393 teaches the preparation of graft copolymer dispersions by employing alkylmercaptan chain transferring agents at concentrations from 0.1 to 2 percent by weight based on the weight of vinyl monomer.
Stable dispersions of polymers in polyols have found broad commercial use in the preparation of polyurethanes. The use of these dispersions, known in the trade as graft or polymer polyols, improves processing and, among other properties, the firmness of the polyurethane products, often expressed as load bearing or modulus. There have been many attempts to improve the products representing the present state of the art. Efforts have been directed towards increasing the amount of polymer that is dispersed in the polyol, the obvious benefit being that firmer polyurethanes can be produced. Two major obstacles have been found: the viscosities of the resulting dispersions were too high and/or relatively high levels of acrylonitrile had to be used in the monomer mixtures employed.
Additionally, it would be desirable if polymer polyols could be prepared which exhibit better stability in terms of less agglomeration. Stability is important to the storage life of the polyols before they are used to make the polyurethane foams since many polymer polyols tend to undergo phase separation if they are not stabilized. Relatively low viscosities and small particle sizes are also important in a good quality polyol to permit it to be pumped easily in high volume foam producing equipment.
U.S. Pat. No. 4,148,840 to Shah and U.S. Pat. No. 4,242,249 to Van Cleve, et al. describe the use of preformed polymer polyols as dispersion stabilizers in the synthesis of SAN dispersion polyols. U.S. Pat. No. 4,148,840 describes preformed polymer polyol stabilizers which have a viscosity of less than 40,000 cP at 25.degree. C. However, these materials arc viscous dispersions or semi-solids, which tend to be difficult to work with.
U.S. Pat. No. 4,172,825 to Shook et al. relates to a process for producing polymeric polyols having high polymer contents. The reference describes a process for making polymer polyols employing a t-butyl peroxide as a free radical initiator. However, the resultant polymer polyols tend to have higher viscosities than those afforded by the present invention.
U.S. Pat. Nos. 4,327,005 and 4,334,049 to Ramlow et al. teach alkylene oxide adducts of styrene/allyl alcohol copolymers as preformed stabilizers for polymer polyols. The stabilizer may take the form of a graft copolymer dispersion or a finely divided solid polymer.
Further, Pizzini et al. in U.S. Pat. No. 3,652,639 describe the use of graft copolymers of acrylonitrile and an unsaturated polyol which are homogeneous, transparent liquids which may be employed directly in the preparation of flexible polyurethane foams. The unsaturated polyol is obtained by reacting an organic compound having both ethylenic unsaturation and a hydroxyl, carboxyl or epoxy group with a polyol. A number of additional patents also teach the use of an acryloyl capped unsaturated polyol copolymerized with styrene and acrylonitrile to produce polymer polyols. These patents include U.S. Pat. Nos. 4,460,715; 4,477,603; 4,640,935; 4,513,124; 4,394,491; and 4,390,645.
More recently, International Publication No. WO87/03886 and U.S. Pat. No. 4,745,153 teach the homo- or co-polymerization of vinyl terminated polyol adducts alone or together with an ethylenically unsaturated monomer or monomer mixture in the presence of an active hydrogen-containing compound as a solvent, and their use as preformed dispersants.
None of the related art, insofar as is known, either alone or in combination, teaches or suggests that highly stable, low viscosity graft polyols can be produced using t-amyl based free radical initiators, particularly in association with a semi-batch or continuous processes.